Generally, a secondary battery refers to a rechargeable battery, while a general battery refers to a non-rechargeable battery. Secondary batteries are widely used for electronic devices such as cellular phones, notebook computers, video cameras, electric vehicles or the like. In particular, a lithium secondary battery has about three times the capacity of a nickel-cadmium battery or a nickel hydrogen battery generally used as power sources of electronic devices, and due to its high energy density per unit weight, the lithium secondary battery is utilized more and more.
A lithium secondary battery generally uses lithium oxide and carbonaceous material as a cathode active material and anode active material, respectively. The lithium secondary battery includes an electrode assembly in which a cathode plate and an anode plate respectively coated with the cathode active material and the anode active material are disposed with a separator being interposed between them, and a battery case which seals and accommodates the electrode assembly together with an electrolyte.
Meanwhile, a lithium secondary battery may be classified into a can type secondary battery where the electrode assembly is included in a metal can and a pouch type battery where the electrode assembly is included in a pouch of an aluminum laminate sheet, depending on the shape of the battery case. Generally, the can type secondary battery is accommodated in a battery can in a state where the cathode plate and the anode plate, namely electrode plates, are rolled, and the pouch type secondary battery is accommodated in a battery can in a state where the electrode plates are stacked or rolled.
FIG. 1 is a perspective view schematically showing a general electrode assembly for a secondary battery in which electrode plates are stacked by folding a separator 10.
Referring to FIG. 1, the general electrode assembly for a secondary battery is configured so that a plurality of cathode plates 20 and a plurality of anode plates 30 face each other with the separator 10 being interposed between them. In addition, a cathode tab 21 is attached to the cathode plate 20, and an anode tab 31 is attached to the anode plate 30. At this time, when being interposed between the cathode plate 20 and the anode plate 30, the separator 10 may be separately provided to each layer. However, for the sake of convenience and structural stability, a single long separator 10 may be provided so as to be folded at the sides of the cathode plate 20 and the anode plate 30, as widely used in the art.
In addition, the electrode assembly configured as above is accommodated in a battery case and used for manufacturing a secondary battery through an electrolyte injecting process, an activating process, a degasing process or the like.
However, if the electrode assembly adopts the folded separator 10 as shown in FIG. 1, an electrolyte may not penetrate and gas may not be discharged through the folded portion of the separator 10.
FIG. 2 is a diagram showing the electrode assembly of FIG. 1 from above.
As shown in FIG. 2, in the general electrode assembly in which the separator 10 is folded, penetration of an electrolyte into the electrode plate and discharge of gas therefrom are inevitably restricted. In other words, in the general electrode assembly, an electrolyte or gas should be injected or discharged at a front portion of the drawing, where an electrode tab is located, which is not blocked by the separator 10, or a portion opposite thereto, as depicted by arrows a and b. In addition, since a side of the electrode plate which is located at the right or left portion of the drawing is blocked by the separator 10, it is impossible for an electrolyte located outside of the electrode assembly to penetrate or gas in the electrode assembly to discharge through
Therefore, in this configuration, it is not easy to impregnate the electrode plate with an electrolyte, and the degasing process cannot perform smoothly. Therefore, the time and costs for producing a secondary battery surely increases, and the performance and life span of the secondary battery are also badly affected.